Ruling Grade

Ruling grade
The maximum grade that controls train size on a given route.
Runaround ...

Ruling grade
The steepest or longest grade on a given section of railroad; it determines the maximum tonnage that can be handled over the territory by a given locomotive.
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Ruling Grade
The point on a run at which the combination of grade and curve resistance makes the train pull hardest and, therefore, "rules" how heavy a load can be given to the locomotive.
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While not qualifying as one of the renowned grades in railroading, it is the ruling grade on the Chicago Subdivision. I have been reduced to 2 MPH on a loaded grain train on this hill.

So, here's a calculation based upon my planned model of Cajon Pass. The ruling grade is 2.2%. Motive power will be 4400hp GE Dash 9's, pulling a train weight of 7000 tons.
Tractive Effort:
(4400 x 308)
25mph ...

See also: Switch, Track, Engine, Locomotive, Grade